Background: Preterm premature rupture of membranes (PROM) continues to be a leading cause of neonatal morbidity and mortality. Preterm PROM occurs in approximately 2% of all pregnancies but is associated with 20% of all perinatal deaths. By far, the most common complication of preterm PROM is related to intra-amniotic infection termed chorioamnionitis. Chorioamnionitis occurs in 6% of preterm deliveries without PROM but is present in at least 27% of preterm deliveries with PROM; it is associated with a fourfold increase in neonatal mortality. Clinical signs of infection are subtle and usually not present in early chorioamnionitis. Currently there are no reliable clinical markers to adequately indicate impending intrauterine infection in these patients. The cytokine interleukin(IL)-6, thought to have an important role in the intrauterine response to infection, has been reported to be elevated in the amniotic fluid of patients with preterm PROM with intra-amniotic infection. Unfortunately, the widespread clinical use of amniotic fluid IL-6 concentrations in the management of preterm PROM patients would be limited due to the technical difficulty of amniocentesis. Recent studies in our laboratory demonstrate a significant rise in serum IL-6 concentrations in patients with preterm PROM and clinical or histologic evidence of infection on the day of delivery.